qmlprieview: fix that init language is the chosen one

* removes language feature from preview service
* it is handled by an extra DebugTranslationService until now
* Qt versions without that extra service can not preview
  languages anymore
* Introduce the use of QmlPreviewRunnerSetting. It makes it
  easier to add more properties in the future
* Language needs an extra handling because it needs
  the loadUrl to find existing languages. So we save
  the language to a m_scheduledInitLanguage and emit
  this after the loadFile call happend.

Change-Id: I7f4aec97f7b61d6b290f225282169da594eb9160
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/qmlpreview/qmldebugtranslationclient.h

@@ -35,19 +35,20 @@ class QMLPREVIEW_EXPORT QmlDebugTranslationClient : public QmlDebug::QmlDebugCli
     Q_OBJECT
 public:
     //needs to be in sync with QQmlDebugTranslationClient in qtdeclarative/src/plugins/qmltooling/qmldbg_preview/qqmldebugtranslationservice.h
-    enum Command {
+    enum class Command {
         ChangeLanguage,
+        MissingTranslationsChecked,
+        EnableElidedTextWarning,
+        DisableElidedTextWarning,
         ChangeWarningColor,
         ChangeElidedTextWarningString,
         SetDebugTranslationServiceLogFile,
-        EnableElidedTextWarning,
-        DisableElidedTextWarning,
         TestAllLanguages
     };
 
     explicit QmlDebugTranslationClient(QmlDebug::QmlDebugConnection *connection);
 
-    void changeLanguage(const QUrl &url, const QString &locale);
+    void changeLanguage(const QUrl &url, const QString &localeIsoCode);
     void changeWarningColor(const QColor &warningColor);
     void changeElidedTextWarningString(const QString &warningString); //is QByteArray better here?
     void changeElideWarning(bool elideWarning);